24hr Flat Earth Visibility Formula is |Latitude| > 90° – |declination| Union Glacier in DecemberAn observer at -80°S such as Union Glacier in December (-23°) will see a 24hr Sun because the formula holds for true.|-80°| > 90° – |-23°|80° > 90°-23°80 > 67true United States in DecemberAn observer at 45°N such as United States … Continue reading 24hr Flat Earth Visibility Formula